Method and arrangement for controlling at least two hydraulic consumers

ABSTRACT

Disclosed are a control arrangement for actuation of at least two hydraulic consumers, and a method for actuation of these consumers. The latter are supplied with pressure medium through the intermediary of a pump, wherein a respective meter-in orifice and a pressure compensator arranged downstream from the latter are provided between the consumers and the pump. In accordance with the invention, adjustment of the pump is performed in dependence on the target values to which the meter-in orifices are set.

The invention relates to a control arrangement for the pressure mediumsupply of at least two hydraulic consumers in accordance with thepreamble of claim 1, and a method for controlling such consumers inaccordance with the preamble of claim 9.

In order to control several consumers, hydraulic systems are frequentlyemployed where the consumers are supplied with pressure medium throughthe intermediary of a variable displacement pump.

Between the variable displacement pump and each consumer a meter-inorifice and a pressure compensator are provided, wherein the latter maybe arranged upstream from the meter-in orifice (flow regulatorprinciple) or downstream from it (flow divider principle).

From EP 0 566 449 A1 a hydraulic control arrangement operating inaccordance with the flow divider principle is known, which employs theload-sensing (LS) principle. In such LS systems, a variable displacementpump is adjusted in dependence on the highest load pressure of theactuated hydraulic consumers, such that the supply pressure is higherthan the highest load pressure by a specific pressure difference. Thepressure medium flows to the two hydraulic consumers via two adjustablemeter-in orifices, the first of which is disposed between a pump lineissuing from the variable displacement pump and a first hydraulicconsumer, and the second of which is disposed between the pump line andthe second hydraulic consumer. By means of the pressure compensatorsarranged downstream from the meter-in orifices (flow divider principle)it is achieved that in the case of a sufficient quantity of suppliedpressure medium, a certain pressure difference exists across themeter-in orifices independently of the load pressures of the hydraulicconsumers, so that the quantity of pressure medium flowing to ahydraulic consumer depends on nothing but the opening cross-section ofthe respective meter-in orifice. If the latter is opened further, agreater quantity of pressure medium must flow across it in order togenerate the particular pressure difference. The variable displacementpump is then adjusted so as to deliver the required quantity of pressuremedium. Accordingly, this is also referred to as flow control accordingto demand.

The pressure compensators arranged downstream from the meter-in orificesare subjected to the pressure downstream from the respective meter-inorifice in the opening direction, and in the closing direction to acontrol pressure which prevails in a rearward control chamber andusually corresponds to the highest load pressure of all the hydraulicconsumers supplied by a same hydraulic pump. If, upon concurrentactuation of several hydraulic consumers, the meter-in orifices areopened to such an extent that the quantity of pressure, medium suppliedfrom the hydraulic pump adjusted to the limit is smaller than the totaldemanded quantity of pressure medium, the quantities of pressure mediumflowing to the single hydraulic consumers are reduced proportionally,independently of the respective load pressure of the hydraulicconsumers. Accordingly, this case is referred to as a control withload-independent flow distribution (LastunabhängigeDurchflussverteilung: LUDV control) (flow divider principle). Because insuch a LUDV control the highest load pressure is furthermore tapped, anda supply pressure higher than the highest load pressure by a particularpressure difference is generated by the pressure medium source, a LUDVcontrol practically is a special case of a load-sensing control.

For several hydraulic consumers at which a respective flow of pressuremedium arrives via a meter-in orifice with an upstream pressurecompensator (flow regulator principle) which is subjected to thepressure upstream from the meter-in orifice in the closing direction,and to the load pressure of the respective hydraulic consumer and acompression spring in the opening direction, it is not possible toobtain a load-independent flow distribution. If several hydraulicconsumers are actuated simultaneously while not being supplied with asufficient quantity of pressure medium delivered from the variabledisplacement pump, only the quantity of pressure medium flowing to thehydraulic consumer having the highest load pressure is reduced.

In the above described LS systems, the variable displacement pump isactuated in dependence on the highest load pressure, so that a pressuremanifests in the pump line which is higher than the highest loadpressure by a pressure difference equivalent to the force of a controlspring of a pump control valve (so-called Δp control of the variabledisplacement pump).

A solution improved in comparison with the document EP 0 566 449 A1mentioned at the outset is disclosed in DE 199 04 616 A1, however theabove described Δp control is also employed in this system. It is adrawback of this control that considerable system losses may be incurreddue to the necessity of raising the pressure supplied by the pump abovethe highest load pressure by the respective above described Δp, for thispressure difference is situated in a range between 20 to 40 bar. It wasmoreover found that the Δp control exhibits a certain susceptibility tovibration, rendering a continuous actuation of the consumers difficult.

In contrast, the invention is based on the objective of furtherdeveloping a hydraulic control arrangement for controlling at least twoconsumers, as well as a method for controlling these consumers, suchthat the energy losses and the susceptibility to vibration are reduced.

With regard to the control arrangement, this object is achieved throughthe features of claim 1, and with regard to the method by the featuresof independent claim 9.

In accordance with the invention, a variable displacement pump (pumphaving a variable capacity) and adjustable meter-in orifices arrangedupstream from each consumer may be actuated proportionally, preferablyelectrically, wherein the variable displacement pump is actuated independence on target values predetermined for the meter-in orifices. Inother words, in contrast with the LS systems described at the outset,the variable displacement pump is adjusted not in dependence on apressure signal corresponding to the highest load pressure, but independence on target values predetermined by an operator so as to movethe consumer, e.g., at a particular velocity. The adjustment of thevariable displacement pump is then performed in dependence on thesetarget values so as to enable it to supply the pre-set target flow ratesto all of the consumers. I.e., the variable displacement pump must beadjusted to a swivel angle at which is delivers precisely this requestedcumulative consumer flow.

Such a system fundamentally constitutes a flow rate control in whichflow rate errors owing to volumetric losses of the pump are not ofimportance, for when the flow rate and thus the velocity of theconsumers is too low, the operator will manually perform a readjustmentand thus compensate the flow rate error. As the variable displacementpump is actuated by a flow rate control independently of the highestload pressure, the system has a substantially lower susceptibility tovibration than the known LS control arrangements.

It is a further advantage of the control arrangement of the inventionand of the method of the invention that in single operation of aconsumer, it is possible to fully open the meter-in orifices outside ofthe fine control range, wherein the flow rate to the consumer isdetermined by the actuation of the variable displacement pump: thethrottling losses at the meter-in orifice are then minimum. In theoperation of several consumers, the throttling losses may be reduced, inaccordance with an advantageous development of the invention, in thatthe meter-in orifice of the one consumer receiving the highest pressuremedium volume flow, i.e., the one consumer set to the highest targetvalue, is opened fully, and the cross-sections of the other meter-inorifices are caused to follow up in accordance with the ratio of thepressure medium flow rates, so that the system losses are minimized incomparison with conventional solutions. This case does, however, notoccur very frequently as a consumer is as a general rule operated atmaximum velocity.

Actuation of the variable displacement pump and of the meter-in orificesis performed through central control means preferably including a datastorage, wherein characteristics of the variable displacement pump andof the meter-in orifices are stored.

The variable displacement pump is preferably provided with a rotationalspeed sensor whereby the current rotational speed of the pump may bedetected, so that the target flow rate may be adjusted in a simplemanner with the aid of the stored characteristics.

The control arrangement in accordance with the invention is preferablyexecuted with anti-cavitation valves through which pressure medium maybe replenished in a low-pressure side of the consumer in the case of apulling load. In this case, in accordance with the solution of theinvention the flow rate of the pump is reduced, so that the systemlosses are further reduced in comparison with conventional solutions.

An acquisition of the target values is preferably performed byevaluating the adjustment of a joystick or by detecting the position ofthe control piston of the meter-in orifice.

Further advantageous developments of the invention are subject matter offurther subclaims.

In the following a preferred practical example of the invention shall beexplained by referring to a circuit diagram.

The FIGURE shows a circuit diagram of a hydraulic control arrangement 1in accordance with the invention, which practically constitutes amodified LUDV system.

The control arrangement in accordance with the invention comprises avariable displacement pump 2 whereby the two or more consumers 4, 6 maybe supplied with pressure medium. Actuation of the consumers 4, 6 takesplace with the aid of a control apparatus, for instance a joystick 8,whereby control signals are output to a control means 10. These signalspractically constitute a command to displace the consumer at aparticular velocity.

The outlet from the variable displacement pump 2 is connected to a pumpline 12 branching into two supply lines 14, 16. In each supply line 14,16 a respective electrically proportionally adjustable meter-in orifice18 or 20 is arranged, downstream of which a respective pressurecompensator 22 or 24 is arranged. The outlets from the two pressurecompensators 22, 24 are connected with the respective consumer via aflow line 26, 28. In the present case, the consumers 4, 6 are hydrauliccylinders, the cylinder chambers of which are connected to the flow line26 or 28. In practice, the meter-in orifices 18, 20 are embodied aselectrically or hydraulically proportionally adjustable directionalcontrol valves. In the present hydraulic circuit diagram, the return anddrain lines connecting the named cylinder chambers 30, 32 with the tankTi the flow cross-sections of which are preferably also opened andclosed by means of the respective proportional valve constituting themeter-in orifice 18, 20, are omitted for the sake of clarity.

The pressure compensators 22, 24 are subjected in the opening directionto the pressure downstream from the respective meter-in orifice 18, 20and in the closing direction to a pressure corresponding to the highestload pressure at the two consumers 4, 6. This highest load pressure istapped via a LS line 34 and a shuttle valve 36 from the one flow line26, 28 at which the highest load pressure prevails.

Actuation of the two meter-in orifices 18, 20 takes place by means ofthe control means 10 as a function of the control signal set at thejoystick 8 (target value).

As was described at the outset, in such a system the pressuresdownstream from the two meter-in orifices 18, 20 are identical, and theratio of the magnitudes of the flow rates to the consumers 4, 6corresponds to the ratio of the opening cross-sections of the twometer-in orifices 18, 20. By means of the downstream pressurecompensator 22, 24, the pressure prevailing downstream from the meter-inorifices 18, 20 is throttled to the respective prevailing load pressure.

The variable displacement pump 2 is in the represented practical exampleexecuted with a pressure sensor for detecting the pump pressure, arotational speed sensor for detecting the pump speed, and a swivel anglesensor for detecting the swivel angle of the pump. In the data storageof the control means the characteristics for the variable displacementpump 2 and for the two proportionally adjustable meter-in orifices 18,20 are moreover stored, so that with the aid of all or some of the abovementioned sensors and of the characteristics, an extremely accurate flowrate control by means of the variable displacement pump 2 is possible.The operation of the control arrangement in accordance with theinvention is as follows:

In order to actuate the two consumers 4, 6, control signals aregenerated by the operator with the aid of one or more joysticks 8 andoutput to the control means 10. For correspondingly actuating theconsumers 4, 6, the variable displacement pump 2 has to provide aparticular pressure medium volume flow corresponding to the sum of thetarget flow rates adjusted by means of the joystick 8. In other words,the variable displacement pump 2 must be adjusted, in dependence on theadjustment of the joystick 8, to a swivel angle at which this cumulativeflow rate is delivered. The corresponding adjustment of the variabledisplacement pump 2 may in a simple manner be achieved in dependence onthe target value by detecting the current pump pressure, the currentpump speed, and the adjusted swivel angle with the aid of the pumpcharacteristic. I.e., in accordance with the invention the pumpcontroller does not receive a pressure signal that corresponds, as arule, to the highest load pressure, but actuation of the variabledisplacement pump is performed solely in dependence on the target valuesadjusted with the aid of the joystick.

In this target value adjustment with the aid of the joystick 8 it ispossible to compensate flow rate errors occurring as a result ofvolumetric losses of the variable displacement pump 2, for the operatorwill immediately perform a readjustment with the aid of the joystick 8if the consumers 4, 6 are not actuated at the desired velocity.

It is another particularity of the invention that in parallel actuationof the consumers 4, 6 through the control means 10, the one consumer 4,6 is determined that has to be supplied with the highest pressure mediumvolume flow. This may be achieved in a simple manner with the aid of thetarget values adjusted at the joystick 8, so that no further sensors arerequired. The meter-in orifice 18, 20 of this consumer 4, 6 to besupplied with the highest pressure medium volume flow is then openedcompletely through the control means 10, and the opening cross-sectionsof the other meter-in orifices 20 or 18 are caused to follow upcorrespondingly, so that the system losses are minimized in comparisonwith conventional solutions. In a case in which only one consumer 4, 6is actuated, the associated meter-in orifice 18 or 20 may be openedfully outside of the fine control range so as to minimize the systemlosses. The pressure medium volume flow to the consumer is thencontrolled solely through the variable displacement pump.

In an advantageous practical example of the invention, the cylinderchambers 30, 32 of the consumers 4, 6 are each connected to the tank Tby a respective anti-cavitation valve, so that pressure medium may bereplenished into the cylinder chambers 30, 32 via these anti-cavitationvalves—which are not represented—in the case of a pulling load(low-pressure side). This pressure in the low-pressure side is detected,and by means of the control means 10 a control signal is output to thevariable displacement pump 2, so that the swivel angle of the variabledisplacement pump 2 is reduced, and no pressure medium is conveyed bythe pump. By this arrangement, the losses may be minimized further incomparison with conventional arrangements.

In the above described practical example, the target values arepredetermined with the aid of a joystick 8. In the case of proportionalvalves including spool path measurement, the target flow rate may alsobe determined on the basis of the path of the valve spool of themeter-in orifice 18, 20, i.e., in this case not the signal adjusted atthe joystick 8 is used directly, but the actual value manifesting at thevalve spools of the meter-in orifices 18, 20 as a result of this signal.

As in the system of the invention a flow rate control is performedthrough the intermediary of the variable displacement pump 2, thesusceptibility to vibration is substantially lower than in thepreviously known solutions. Thanks to the suppression of the LSindicator lines leading to the control valve, the complexity in terms ofcontrol technology may be reduced in comparison with the Δp systemsdescribed at the outset.

In accordance with the above description, the variable displacement pumpmay be realized such that the geometric displacement volume isadjustable, however it is also possible to employ constant or variabledisplacement pumps having a variable speed drive.

Disclosed are a control arrangement for actuation of at least twohydraulic consumers, and a method for actuation of these consumers. Thelatter are supplied with pressure medium through the intermediary of apump, wherein a respective meter-in orifice and a pressure compensatorarranged downstream from the latter are provided between the consumersand the pump. In accordance with the invention, adjustment of the pumpis performed in dependence on the target values to which the meter-inorifices are set.

LIST OF REFERENCE SYMBOLS

-   1 control arrangement-   2 variable displacement pump-   4 consumer-   6 consumer-   8 joystick-   10 control means-   12 pump line-   14 supply line-   16 supply line-   18 meter-in orifice-   20 meter-in orifice-   22 pressure compensator-   24 pressure compensator-   26 flow line-   28 flow line-   30 cylinder chamber-   32 cylinder chamber-   34 LS line-   36 shuttle valve

1. A control arrangement for the pressure medium supply of at least twohydraulic consumers, comprising a pump having a variable capacity, andcomprising two adjustable meter-in orifices, a first one of which isdisposed between a supply line issuing from the pump and a firsthydraulic consumer, and the second one of which is disposed between asupply line and a second hydraulic consumer, and comprising two pressurecompensators, a first one of which is arranged downstream from the firstmeter-in orifice, and the second one of which is arranged downstreamfrom the second meter-in orifice, and the control pistons of which areadapted to be subjected on a front side to the pressure downstream fromthe respective meter-in orifice in the opening direction, and in theclosing direction to the highest load pressure or to a pressure derivedtherefrom, wherein the pump and the meter-in orifices are adjustable,preferably proportionally, characterized by a control means foroutputting a control signal to the pump in dependence on the targetvalues predetermined for the meter-in orifices.
 2. The controlarrangement in accordance with claim 1, wherein the flow rate of thepump may be adjusted electrically by means of proportional solenoids. 3.The control arrangement in accordance with claim 1, wherein the meter-inorifice having the highest target value may be opened fully with the aidof the control means, and the other meter-in orifices may be caused tofollow up accordingly.
 4. The control arrangement in accordance withclaim 1, characterized in that the control means include a data storagewherein the characteristics of the variable displacement pump and of themeter-in orifices are stored.
 5. The control arrangement in accordancewith claim 1, characterized in that the pump is an axial piston pump. 6.The control arrangement in accordance with claim 1, comprising arotational speed sensor for detecting the pump speed.
 7. The controlarrangement in accordance with claim 1, comprising anti-cavitationvalves whereby the pressure medium chambers of the consumers may beconnected with a tank, so that pressure medium may be replenished intothe pressure medium chambers in the case of a pulling load.
 8. Thecontrol arrangement in accordance with claim 1, wherein the targetvalues are detected in dependence on the adjustment of a joystick or independence on the control piston position of the meter-in orifices.
 9. Amethod for controlling at least two hydraulic consumers adapted to besupplied with pressure medium through the intermediary of avariable-capacity pump, wherein to each consumer a meter-in orifice isassociated, that are provided between the pump and the respectiveconsumer and downstream of which a respective pressure compensator isarranged, the control piston of which is subjected to the pressurebehind the upstream meter-in orifice in the opening direction, and inthe closing direction to the highest load pressure or to a pressurederived therefrom, characterized in that the pump is operated independence on the target values predetermined for the meter-in orifices.10. The method in accordance with claim 9, wherein the meter-in orificeto be set to the highest target value is opened fully, and the othermeter-in orifices are caused to follow up accordingly.
 11. The method inaccordance with claim 9, wherein the flow rate of the pump is reducedand pressure medium is replenished via anti-cavitation valves to thelow-pressure side of the consumers in the case of a pulling load.